WO2014175352A1 - リチウムイオン二次電池用正極及びそれを含むリチウムイオン二次電池 - Google Patents
リチウムイオン二次電池用正極及びそれを含むリチウムイオン二次電池 Download PDFInfo
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- WO2014175352A1 WO2014175352A1 PCT/JP2014/061474 JP2014061474W WO2014175352A1 WO 2014175352 A1 WO2014175352 A1 WO 2014175352A1 JP 2014061474 W JP2014061474 W JP 2014061474W WO 2014175352 A1 WO2014175352 A1 WO 2014175352A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Definitions
- the present invention relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery including the same. More specifically, the present invention relates to a positive electrode for a lithium ion secondary battery having excellent cycle characteristics and a lithium ion secondary battery including the same.
- a lithium ion secondary battery has a positive electrode, a negative electrode, an electrolyte solution, a separator, and an exterior material as its main components.
- the positive electrode includes a positive electrode active material, a conductive material, a current collector, and a binder (binder).
- a layered transition metal oxide typified by LiCoO 2 is used as the positive electrode active material.
- the layered transition metal oxide easily causes oxygen desorption at a relatively low temperature of about 150 ° C. in a fully charged state, and the thermal desorption reaction of the battery can occur due to the oxygen desorption. Therefore, when a battery having such a positive electrode active material is used for a portable electronic device, there is a risk that an accident such as heat generation or ignition of the battery may occur.
- lithium iron phosphate LiFePO 4
- derivatives thereof having an olivine type structure that is stable and does not release oxygen when abnormal and is cheaper than LiCoO 2 are expected.
- Patent Document 1 describes LiFe 1-x Zr x P 1-y Si y O in which the Fe site is substituted by Zr and the P site is substituted by Si. 4 has been reported.
- the inventors of the present invention have studied, (I) The lattice constants a, b and c of the unit cell of the lithium-containing metal oxide as the positive electrode active material are in a specific range. (Ii) The porosity of the positive electrode active material layer is in a specific range. (Iii) When the total value of the volume of the lithium-containing metal oxide and the volume of the conductive material is within a specific range, it has been found that a positive electrode for a lithium secondary battery with improved cycle characteristics can be provided, leading to the present invention. .
- the positive electrode active material layer has the following general formula (1) LiFe 1-x Zr x P 1-y Si y O 4 (1) (However, 0 ⁇ x ⁇ 1 and 0 ⁇ y ⁇ 1)
- the unit cell has a lattice constant of 10.326 ⁇ a ⁇ 10.335, 6.006 ⁇ b ⁇ 6.012, 4.685 ⁇ c ⁇ 4.714, Lithium ions in which the total volume of the lithium-containing metal oxide and the volume of the conductive material is 1.61 ⁇ 10 ⁇ 3 to 6.46 ⁇ 10 ⁇ 3 cm 3 / cm 2 per unit area of the current collector A positive electrode for a secondary battery is provided.
- the lithium ion secondary battery provided with the said positive electrode, a negative electrode, and the separator located between the said positive electrode and the said negative electrode is provided.
- the present invention can provide a positive electrode capable of improving the cycle characteristics of a lithium ion secondary battery and a lithium ion secondary battery having improved cycle characteristics.
- the positive electrode active material layer has voids with a volume ratio of 30 to 52%.
- the volume of the lithium-containing metal oxide and the volume of the conductive material are 1: 0.06.
- the total value of the volume of the lithium-containing metal oxide and the volume of the conductive material has a ratio of 40 to 65% of the volume of the positive electrode active material layer (4)
- x and y are (5) in the range of 0.015 ⁇ x ⁇ 0.095 and 0.025 ⁇ y ⁇ 0.19, when x and y have any of a ratio of 1: 1 to 2, lithium ions
- a positive electrode capable of further improving the cycle characteristics of the secondary battery and a lithium ion secondary battery having improved cycle characteristics can be provided.
- the positive electrode includes a current collector and a positive electrode active material layer including a lithium-containing metal oxide as a positive electrode active material formed on at least one surface of the current collector.
- Lithium-containing metal oxide The lithium-containing metal oxide has the following general formula (1): LiFe 1-x Zr x P 1-y Si y O 4 (1) (However, 0 ⁇ x ⁇ 1 and 0 ⁇ y ⁇ 1) It has a unit cell represented by
- the valence of Fe and Zr is not particularly limited. Specifically, Fe can take 2 to 4 and 6 valences, and Zr can take 2 to 4 valences. Fe and Zr can use a metal element having a single valence, and a mixture of metal elements having a plurality of valences can also be used. In addition, when using a mixture, the valence for prescribing x in General formula (1) means an average value for convenience. From the viewpoint of improving the insertion and desorption properties of Li, it is preferable to use a bivalent Fe. Zr is preferably tetravalent from the viewpoint of little change in valence during the production of the lithium-containing metal oxide and during charge and discharge.
- x can take a range of 0 ⁇ x ⁇ 1, and y can take a range of 0 ⁇ y ⁇ 1.
- x is preferably in the range of 0.015 ⁇ x ⁇ 0.095 and / or y is preferably in the range of 0.025 ⁇ y ⁇ 0.19, and 0.025 ⁇ x ⁇ More preferably, it is in the range of 0.05 and / or 0.025 ⁇ y ⁇ 0.10.
- x and y preferably have a ratio of 1: 1 to 2 from the viewpoint of further improving the cycle characteristics.
- Most lithium-containing metal oxides having the composition of the general formula (1) have an olivine type structure, but may have a configuration not having an olivine type structure.
- the unit cell of the lithium-containing metal oxide has a lattice constant of 10.326 ⁇ a ⁇ 10.335, 6.006 ⁇ b ⁇ 6.012, 4.685 ⁇ c ⁇ 4.714. .
- the inventors of the present invention have surprisingly found that the cycle characteristics can be improved by having a lattice constant in these ranges. More preferable lattice constants are 10.326 ⁇ a ⁇ 10.330, 6.006 ⁇ b ⁇ 6.008, 4.685 ⁇ c ⁇ 4.694.
- the lithium-containing metal oxide preferably has an average particle size of 0.3 to 30 ⁇ m. A more preferable average particle diameter is 3 to 18 ⁇ m.
- Lithium-containing metal oxide is prepared by using carbonate, hydroxide, chloride, sulfate, acetate, oxide, oxalate, nitrate, alkoxide of each element as a raw material. It can manufacture by using the combination of these.
- the raw material may contain hydration water.
- methods such as a firing method, a solid phase method, a sol-gel method, a melt quench method, a mechanochemical method, a coprecipitation method, a hydrothermal method, and a spray pyrolysis method can be used.
- a firing method under an inert atmosphere for example, a nitrogen atmosphere
- firing conditions are 400 to 650 ° C. for 1 to 24 hours
- a near the upper limit can be achieved by increasing the amount of Zr raw material (Zr source), and a near the lower limit can be achieved by decreasing the amount of Zr raw material (Zr source).
- b near the upper limit can be achieved by increasing the amount of Zr raw material (Zr source) charged, and b near the lower limit can be achieved by decreasing the amount of Zr raw material (Zr source) charged.
- c near the upper limit can be achieved by increasing the amount of Zr raw material (Zr source) charged, and c near the lower limit can be achieved by decreasing the amount of Zr raw material (Zr source) charged.
- the surface of the lithium-containing metal oxide may be coated with carbon in order to improve conductivity.
- the coating may be the entire surface of the lithium-containing metal oxide or a part thereof.
- the carbon coating method is not particularly limited, and a known method can be used.
- the raw material of a lithium containing metal oxide can mix the compound used as a carbon source, and can coat
- the compound serving as the carbon source it is necessary to use a compound that does not prevent the raw material from changing to a lithium-containing metal oxide.
- examples of such compounds include sucrose, fructose and the like for saccharides.
- examples of polyethers include polyethylene glycol and polypropylene glycol.
- any polymer containing carbon such as polyvinyl alcohol, polyacrylamide, carboxymethyl cellulose, polyvinyl acetate, etc. can be used.
- the carbon source compound is preferably used in the range of 5 to 30% by weight with respect to the total of the lithium-containing metal oxide raw material.
- the positive electrode active material layer includes at least the lithium-containing metal oxide and the conductive material as the positive electrode active material.
- the positive electrode active material layer has voids with a volume of 0.82 ⁇ 10 ⁇ 3 to 7.87 ⁇ 10 ⁇ 3 cm 3 / cm 2 per unit area of the current collector. When the void volume is less than 0.82 ⁇ 10 ⁇ 3 cm 3 / cm 2 , the cycle characteristics may be deteriorated due to the precipitation of the electrolytic solution in the void due to the side reaction and the movement of lithium being inhibited. is there.
- the volume of the gap can be adjusted, for example, by the following method. When increasing the volume of the gap, it can be adjusted by increasing the press interval at the time of pressing, and when decreasing it, it can be adjusted by decreasing the press interval at the time of pressing.
- the positive electrode active material layer preferably has voids with a volume ratio of 30 to 52%.
- the volume ratio is less than 30%, the cycle characteristics may be deteriorated due to the lithium migration being inhibited by the precipitates caused by the side reaction of the electrolyte in the gap. If it is larger than 52%, the conductive path is insufficient and the rate characteristics are lowered, and the energy density of the battery may be lowered.
- a more preferable volume ratio is 34 to 48%.
- the positive electrode active material layer preferably has a volume of 2.80 ⁇ 10 ⁇ 3 to 15.8 ⁇ 10 ⁇ 3 cm 3 / cm 2 per unit area of the current collector.
- the volume is less than 2.80 ⁇ 10 ⁇ 3 cm 3 / cm 2
- the capacity per electrode decreases, so the number of current collectors included in the battery, separators, etc. when producing a battery of a certain capacity
- the manufacturing cost increases, and in addition, the capacity density may decrease.
- it is larger than 15.8 ⁇ 10 ⁇ 3 cm 3 / cm 2
- a more preferable volume is 4.17 ⁇ 10 ⁇ 3 to 13.2 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- the total value of the volume of the lithium-containing metal oxide and the volume of the conductive material is 1.61 ⁇ 10 ⁇ 3 to 6.46 ⁇ 10 ⁇ 3 cm 3 / cm 2 per unit area of the current collector.
- the capacity per electrode decreases. Therefore, when manufacturing a battery with a certain capacity, the number of current collectors and separators included in the battery As a result, the manufacturing cost increases, and in addition, the capacity density may decrease.
- an active material layer becomes thick, the resistance of the thickness direction increases, and rate characteristics may fall.
- a preferred total value is 2.26 ⁇ 10 ⁇ 3 to 4.85 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- the volume of the lithium-containing metal oxide is preferably 1.40 ⁇ 10 ⁇ 3 to 5.80 ⁇ 10 ⁇ 3 cm 3 / cm 2 per unit area of the current collector.
- the volume is less than 1.40 ⁇ 10 ⁇ 3 cm 3 / cm 2
- the capacity per electrode decreases, so the number of current collectors included in the battery, separators, etc. when producing a battery with a certain capacity
- the manufacturing cost increases, and in addition, the capacity density may decrease.
- it is larger than 5.80 ⁇ 10 ⁇ 3 cm 3 / cm 2 , it may be necessary to use an excessive amount of conductive material in order to obtain a sufficient conductive contact between the lithium-containing oxides.
- a more preferable total value is 2.02 ⁇ 10 ⁇ 3 to 4.35 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- the volume of the conductive material is preferably 0.16 ⁇ 10 ⁇ 3 to 0.67 ⁇ 10 ⁇ 3 cm 3 / cm 2 per unit area of the current collector.
- the volume is less than 0.16 ⁇ 10 ⁇ 3 cm 3 / cm 2 , the conductive contact between the lithium-containing oxides may be insufficient, the resistance of the active material layer may increase, and the rate characteristics may deteriorate.
- it is larger than 0.67 ⁇ 10 ⁇ 3 cm 3 / cm 2 , the number of conductive material particles in the active material layer increases, so that an excessive amount of binder may be required to obtain a contact between the particles.
- a more preferable total value is 0.23 ⁇ 10 ⁇ 3 to 0.50 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- the volume of the lithium-containing metal oxide and the volume of the conductive material are preferably in a ratio of 1: 0.06 to 0.23.
- the volume ratio of the conductive material is less than 0.06, the conductive contact between the lithium-containing oxides may be insufficient, the resistance of the active material layer may increase, and the rate characteristics may deteriorate.
- the ratio is larger than 0.23, the number of conductive material particles in the active material layer increases, so that an excessive amount of binder may be required to obtain a contact between the particles.
- a more preferred ratio is 1: 0.08 to 0.16.
- the total value of the volume of the lithium-containing metal oxide and the volume of the conductive material is preferably 40 to 65% of the volume of the positive electrode active material layer.
- the total value is less than 40%, the number of conductive contacts between particles in the active material layer is reduced, the conductive path is insufficient, the rate characteristics are lowered, and the energy density of the battery may be lowered. If it is larger than 65%, the gap in the active material layer becomes small, and the lithium transfer is hindered by precipitates due to side reactions of the electrolyte in the gap, so that the cycle characteristics may be deteriorated.
- a more preferable total value is 46 to 55%.
- the said volume is a value calculated from the average particle diameter of the lithium containing metal oxide and electrically conductive material in a positive electrode active material layer, The calculation method is described in the column of an Example.
- the positive electrode active material layer can be produced, for example, by a known method such as applying a slurry in which a lithium-containing metal oxide, a conductive material, and a binder are mixed in an organic solvent to a current collector.
- a slurry in which a lithium-containing metal oxide, a conductive material, and a binder are mixed in an organic solvent to a current collector.
- the conductive material acetylene black, carbon, graphite, natural graphite, artificial graphite, needle coke, or the like can be used.
- Binders include (meth) acrylic resins, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene butadiene rubber, acrylonitrile-butadiene rubber, fluoro rubber, polyvinyl acetate, Polyethylene, nitrocellulose, etc. can be used.
- carboxymethyl cellulose polyvinyl alcohol, polyvinyl pyrrolidone and the like can be used.
- organic solvent N-methyl-2-pyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. are used. be able to.
- foamed (porous) metal having continuous pores, metal formed in a honeycomb shape, sintered metal, expanded metal, non-woven fabric, plate, foil, perforated plate, perforated foil, etc. are used. be able to.
- the thickness of the positive electrode active material layer is preferably about 0.01 to 2 mm. If it is too thick, the conductivity is lowered, and if it is too thin, the capacity per unit area is lowered. In addition, you may compress the positive electrode active material layer obtained by application
- Lithium ion secondary battery The lithium ion secondary battery of this invention is equipped with the said positive electrode, a negative electrode, and the separator located between a positive electrode and a negative electrode.
- the negative electrode includes a negative electrode active material layer.
- the negative electrode active material layer can be produced by a known method. Specifically, it can be produced in the same manner as described in the method for producing the positive electrode active material layer. That is, after mixing with the binder, the conductive material, the thickener, and the negative electrode active material described in the method for preparing the positive electrode active material layer, the mixed powder is formed into a sheet shape, and the formed body is made of stainless steel, copper, or the like. What is necessary is just to crimp
- a known material can be used as the negative electrode active material.
- the potential for lithium insertion / extraction is close to the deposition / dissolution potential of metallic lithium.
- a typical example is a carbon material such as natural or artificial graphite in the form of particles (scale-like, lump-like, fibrous, whisker-like, spherical, pulverized particles, etc.).
- the artificial graphite include graphite obtained by graphitizing mesocarbon microbeads, mesophase pitch powder, isotropic pitch powder, and the like. Also, graphite particles having amorphous carbon attached to the surface can be used.
- lithium transition metal oxide lithium transition metal nitride, transition metal oxide, silicon oxide, and the like can be used as the negative electrode active material.
- Li 4 Ti 5 O 12 is more preferable because of high potential flatness and small volume change due to charge and discharge.
- Nonaqueous electrolyte A lithium ion secondary battery usually includes a nonaqueous electrolyte between a positive electrode and a negative electrode.
- a nonaqueous electrolyte for example, an organic electrolyte, a gel electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt, or the like can be used.
- organic electrolytes are generally used from the viewpoint of battery manufacturability.
- the organic electrolyte contains an electrolyte salt and an organic solvent.
- organic solvents examples include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC) and butylene carbonate, and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, and dipropyl carbonate.
- cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC) and butylene carbonate
- chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, and dipropyl carbonate.
- Lactones such as ⁇ -butyrolactone (GBL) and ⁇ -valerolactone, furans such as tetrahydrofuran and 2-methyltetrahydrofuran, diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, Examples include ethers such as dioxane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, and methyl acetate. One or more of these can be used in combination. Moreover, since cyclic carbonates such as PC, EC and butylene carbonate are high-boiling solvents, they are suitable as solvents to be mixed with GBL.
- cyclic carbonates such as PC, EC and butylene carbonate are high-boiling solvents, they are suitable as solvents to be mixed with GBL.
- Examples of the electrolyte salt include lithium borofluoride (LiBF 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium trifluoroacetate (LiCF 3 COO), lithium bis (trifluoro) Examples thereof include lithium salts such as romethanesulfone) imide (LiN (CF 3 SO 2 ) 2 ), and one or more of these may be used in combination.
- the salt concentration of the electrolytic solution is preferably 0.5 to 3 mol / l.
- separator examples include porous materials and nonwoven fabrics.
- the material of the separator the above-described one that does not dissolve or swell in the organic solvent contained in the electrolyte is preferable.
- Specific examples include polyester polymers, polyolefin polymers (for example, polyethylene and polypropylene), ether polymers, and inorganic materials such as glass.
- a lithium ion secondary battery includes a laminate including, for example, a positive electrode, a negative electrode, and a separator sandwiched between them.
- the laminate may have, for example, a strip-like planar shape.
- the laminate may be wound.
- One or more of the laminates are inserted into the battery container.
- the positive electrode and the negative electrode are connected to the external conductive terminal of the battery.
- the battery container is sealed to block the positive electrode, the negative electrode, and the separator from the outside air.
- the sealing method is generally a method in which a lid having a resin packing is fitted into the opening of the battery container and the battery container and the lid are caulked.
- a method of attaching a lid called a metallic sealing plate to the opening and performing welding can be used.
- a method of sealing with a binder and a method of fixing with a bolt via a gasket can also be used.
- a method of sealing with a laminate film in which a thermoplastic resin is attached to a metal foil can also be used. An opening for electrolyte injection may be provided at the time of sealing.
- the average particle size of the single-phase powder means a value D50 at which the cumulative degree of particle volume is 50%, and is a value measured using a laser diffraction / scattering particle size distribution measuring apparatus.
- the lattice constant was determined by the following procedure.
- the positive electrode active material A1 was pulverized in an agate mortar, and a powder X-ray diffraction pattern was obtained using an X-ray analyzer MiniFlexII manufactured by Rigaku Corporation.
- the measurement conditions were set at a voltage of 30 kV, a current of 15 mA, a divergence slit of 1.25 °, a light receiving slit of 0.3 mm, a scattering slit of 1.25 °, a range of 2 ⁇ of 10 ° to 90 °, and a step of 0.02 °
- the measurement time for each step was adjusted so that the peak intensity was 800-1500.
- Positive electrode active material A2 Except that each raw material was weighed so that the molar ratio of Li: Fe: Zr: P: Si was 1: 0.975: 0.025: 0.975: 0.025, the same as the positive electrode active material A1.
- a positive electrode active material A2 (average particle diameter of 9.2 ⁇ m and true density of 3.45 g / cm 3 ) was obtained.
- Positive electrode active material A3 Except that each raw material was weighed so that the molar ratio of Li: Fe: Zr: P: Si was 1: 0.975: 0.025: 0.95: 0.05, the same as the positive electrode active material A1.
- a positive electrode active material A3 (average particle diameter of 9.2 ⁇ m and true density of 3.45 g / cm 3 ) was obtained.
- Positive electrode active material A4 Except that each raw material was weighed so that the molar ratio of Li: Fe: Zr: P: Si was 1: 0.965: 0.035: 0.965: 0.035, it was the same as that of the positive electrode active material A1.
- a positive electrode active material A4 (average particle diameter of 9.2 ⁇ m and true density of 3.45 g / cm 3 ) was obtained.
- Positive electrode active material A5 Except that each raw material was weighed so that the molar ratio of Li: Fe: Zr: P: Si was 1: 0.905: 0.095: 0.81: 0.19, the same as the positive electrode active material A1.
- a positive electrode active material A5 (average particle size 9.2 ⁇ m and true density 3.45 g / cm 3 ) was obtained.
- Positive electrode active material A6 Except that each raw material was weighed so that the molar ratio of Li: Fe: Zr: P: Si was 1: 0.985: 0.015: 0.97: 0.03, it was the same as that of the positive electrode active material A1.
- a positive electrode active material A6 (average particle size: 9.2 ⁇ m and true density: 3.45 g / cm 3 ) was obtained.
- Positive electrode active material A7 Commercially available LiFePO 4 (manufactured by Sumitomo Osaka Cement Co., Ltd.) was used as the positive electrode active material A7 (average particle size 9.2 ⁇ m and true density 3.45 g / cm 3 ).
- Positive electrode active material A8 Except that each raw material was weighed so that the molar ratio of Li: Fe: Zr: P: Si was 1: 0.9: 0.1: 0.8: 0.2, the same as the positive electrode active material A1.
- a positive electrode active material A8 (average particle diameter of 9.2 ⁇ m and true density of 3.45 g / cm 3 ) was obtained.
- Positive electrode active material A9 Except that each raw material was weighed so that the molar ratio of Li: Fe: Zr: P: Si was 1: 0.925: 0.075: 0.85: 0.15, it was the same as that of the positive electrode active material A1.
- a positive electrode active material A9 (average particle diameter 9.2 ⁇ m and true density 3.45 g / cm 3 ) was obtained.
- Table 2 summarizes the Zr / Si molar ratio, lattice constant, true density, and average particle size of the positive electrode active material.
- Example 1 Positive electrode
- the positive electrode active material A1 acetylene black (conductive material, average particle size 0.035 ⁇ m, true density 1.8 g / cm 3 , manufactured by Denki Kagaku Kogyo), acrylic resin (binder, solid content concentration 29. 9% by weight, manufactured by JSR), carboxymethylcellulose (thickener, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) at a weight (g) of 100: 6: 27: 1.2, Fillmix 80-50 (Primix) The mixture was stirred and mixed with 78.8 g of ion exchanged water at room temperature to obtain an aqueous positive electrode paste.
- This positive electrode paste was applied on both surfaces of a rolled aluminum foil (thickness: 20 ⁇ m) using a die coater.
- the coating amount (solid content) on one side was 5: 0.30: 0.35: 0.003 mg / cm 2 in the order of the positive electrode active material, acetylene black, acrylic resin, and carboxymethylcellulose.
- the obtained coating film was dried in air at 100 ° C. for 10 minutes (68 ⁇ m thickness when dried) and pressed to obtain a positive electrode P1 (coating layer) having a positive electrode active material layer having a thickness of 48 ⁇ m on the current collector. Work surface size: 28 mm (length) ⁇ 28 mm (width)) was obtained.
- the total value of the positive electrode active material volume and the conductive material volume is 1.62 ⁇ 10 ⁇ 3 cm 3 / cm 2
- the void volume of the positive electrode active material layer is 0.84 ⁇ 10 ⁇ 3 cm 3 / cm 2.
- the volume of the positive electrode active material means an integrated value of the average particle diameter and the number of particles of the positive electrode active material per unit area of the current collector.
- the volume of the conductive material means an integrated value of the average particle diameter and the number of particles of the positive electrode active material per unit area of the current collector.
- the average particle diameter of the conductive material means a value obtained by the same method as that for the positive electrode active material.
- the void volume of the positive electrode active material layer means a value obtained by subtracting the volumes of the positive electrode active material and the conductive material, which are solid components constituting this layer, from the volume of the positive electrode active material layer.
- the volume of the positive electrode active material layer means the integrated value of the thickness x length x width of this layer.
- Negative electrode Natural graphite manufactured by Hitachi Chemical Co., Ltd.
- styrene butadiene rubber binder, solid concentration 40.1% by weight, manufactured by Nippon Zeon Co., Ltd.
- carboxymethyl cellulose manufactured by Daicel Corporation
- An aqueous negative electrode paste was obtained by stirring and kneading with 100 g of ion-exchanged water at room temperature using a biaxial planetary mixer (manufactured by Primex) at a weight (g) of 2: 1.
- This negative electrode paste was applied on one side of a rolled copper foil (thickness: 10 ⁇ m) using a die coater.
- the obtained coating film was dried in air at 100 ° C. for 10 minutes and pressed to form a negative electrode having a negative electrode active material layer having a thickness of 20 ⁇ m on the current collector (coating surface size: 30 mm (vertical) ⁇ 30 mm (horizontal)) was obtained.
- FIG. 1 (b) Battery The battery shown in FIG. 1 (b) was produced according to the procedure shown in FIG. 1 (a). First, the positive electrode 1 and the negative electrode 2 were dried under reduced pressure at 130 ° C. for 24 hours, and then placed in a glow box in a dry Ar atmosphere. Next, an aluminum tab lead 4 with an adhesive film 3 was ultrasonically welded to the positive electrode 1, and a nickel tab lead 6 with an adhesive film 5 was ultrasonically welded to the negative electrode 2.
- a separator (microporous membrane, size: 30 mm (vertical) ⁇ 30 mm (horizontal) ⁇ 25 ⁇ m (thickness), manufactured by Polypore)) 9 is loaded so that the coating surface 7 of the negative electrode 2 is hidden, and the coating surface A single cell 10 was fabricated by stacking the positive electrodes 1 so as to overlap each other. 8 represents the coated surface of the positive electrode 1.
- the single cell 11 was sandwiched between the aluminum laminate films 11 and 12, and the three sides of the aluminum laminate films 11 and 12 were thermally welded so as to sandwich the adhesive films 3 and 5 of the tab leads 4 and 6.
- An electrolyte solution in which LiPF 6 is dissolved to a concentration of 1 mol / L in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 2 is poured into the single cell 10 from one side of the unwelded side. Liquid. After the injection, the last side of the aluminum laminate film 11 and 12 bags was heat-sealed under a reduced pressure of 10 kPa to obtain a battery 14.
- Reference numeral 13 denotes a heat fusion part.
- the amount of the electrolyte solution injected is appropriately determined according to the thickness of the electrode used in each battery (total value of the positive electrode and the negative electrode), and the electrolyte solution is added to the positive electrode, the negative electrode, and the separator of the actually fabricated battery. The amount was sufficient to penetrate.
- Example 2 A battery was obtained in the same manner as in Example 1 except that the positive electrode active material A2 was used and the volume of the voids in the positive electrode active material layer was 1.56 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Example 3 A battery was obtained in the same manner as in Example 1 except that the positive electrode active material A3 was used and the volume of the voids in the positive electrode active material layer was 1.76 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Example 4 The positive electrode active material A4 was used, and the coating amount (solid content) on one side was 8: 0.48: 0.56: 0.005 mg / cm 2 in the order of the positive electrode active material, acetylene black, acrylic resin, and carboxymethylcellulose.
- a battery was obtained in the same manner as in Example 1 except that the volume of the voids in the positive electrode active material layer was 2.86 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Example 5 The positive electrode active material A5 was used, and the coating amount (solid content) on one side was 8: 0.48: 0.56: 0.005 mg / cm 2 in the order of the positive electrode active material, acetylene black, acrylic resin, and carboxymethylcellulose.
- a battery was obtained in the same manner as in Example 1 except that the volume of the voids in the positive electrode active material layer was 2.86 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Example 6 The coating amount on one side (solid content) was 14.2: 0.85: 0.99: 0.009 mg / cm 2 in the order of positive electrode active material, acetylene black, acrylic resin, carboxymethylcellulose, and the positive electrode active material layer A battery was obtained in the same manner as in Example 1 except that the volume of the gap was 5.07 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Example 7 The positive electrode active material A6 was used, and the coating amount (solid content) on one side was 12: 0.72: 0.83: 0.008 mg / cm 2 in the order of the positive electrode active material, acetylene black, acrylic resin, and carboxymethylcellulose.
- a battery was obtained in the same manner as in Example 1 except that the volume of the voids in the positive electrode active material layer was 4.57 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Example 8 The coating amount (solid content) on one side was set to 18.4: 1.10: 1.28: 0.012 mg / cm 2 in the order of positive electrode active material, acetylene black, acrylic resin, and carboxymethylcellulose, and the positive electrode active material layer A battery was obtained in the same manner as in Example 1 except that the void volume was 7.84 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Example 9 The coating amount (solid content) on one side was set to 19.8: 1.19: 1.38: 0.012 mg / cm 2 in the order of positive electrode active material, acetylene black, acrylic resin, carboxymethylcellulose, and the positive electrode active material layer A battery was obtained in the same manner as in Example 1 except that the volume of the void was 7.22 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Example 1 A battery was obtained in the same manner as in Example 1 except that the volume of the gap in the positive electrode active material layer was 0.66 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Comparative Example 2 The coating amount (solid content) on one side was set to 18.4: 1.10: 1.28: 0.012 mg / cm 2 in the order of positive electrode active material, acetylene black, acrylic resin, and carboxymethylcellulose, and the positive electrode active material layer
- a battery was obtained in the same manner as in Example 1 except that the void volume was 7.97 ⁇ 10 ⁇ 3 cm 3 / cm 2 .
- Rate characteristics The produced battery is charged to 3.6 V at 0.1 C in a 25 ° C. environment, discharged to 2.0 V at 0.1 C, and the capacity of 0.1 C is increased to 3.6 V at 0.1 C. By charging and discharging to 2.0V at 1C, the 1C capacity was measured, and the rate characteristics (1C / 0.1C) were calculated. In addition, the capacity
- Cycle characteristics The process of charging the prepared battery to 3.6 V at 1 C and discharging to 2.0 V at 1 C in a 25 ° C. environment is assumed to be 1 cycle, repeating 3500 cycles, and the discharge capacity of the first cycle and 3500 cycles The cycle characteristics at 3500 cycles were calculated by comparing the discharge capacities of the eyes. The results obtained are shown in Table 3.
- the void volume is 0.82 ⁇ 10 ⁇ 3 to 7.87 ⁇ 10 ⁇ 3 cm 3 / cm 2
- the lattice constants are 10.326 ⁇ a ⁇ 10.335, 6.006 ⁇ b ⁇ 6. 012, 4.685 ⁇ c ⁇ 4.714
- the total value of the volume of the positive electrode active material and the volume of the conductive material is 1.61 ⁇ 10 ⁇ 3 to 6.46 ⁇ 10 ⁇ 3 cm 3 / cm 2 It can be seen that the rate characteristic and the cycle characteristic are improved.
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Abstract
Description
リチウムイオン二次電池は、その主たる構成要素として正極、負極、電解液、セパレータ及び外装材を有する。また、上記正極は、正極活物質、導電材、集電体及びバインダー(結着剤)により構成される。
(i)正極活物質としてのリチウム含有金属酸化物の単位格子の格子定数a、b及びcが、特定の範囲であること
(ii)正極活物質層の空隙率が、特定の範囲であること
(iii)リチウム含有金属酸化物の容積と導電材の容積の合計値が、特定の範囲であること
で、サイクル特性が向上したリチウム二次電池用正極を提供できることを見出し、本発明に至った。
前記正極活物質層が、下記一般式(1)
LiFe1-xZrxP1-ySiyO4 (1)
(但し、0<x<1であり、0<y<1である)
で表される単位格子を有するリチウム含有金属酸化物と、導電材とを含む層であり、集電体の単位面積当たり、0.82×10-3~7.87×10-3cm3/cm2の容積の空隙を有し、
前記単位格子が、10.326≦a≦10.335、6.006≦b≦6.012、4.685≦c≦4.714の格子定数を有し、
前記リチウム含有金属酸化物の容積と導電材の容積の合計値が、集電体の単位面積当たり、1.61×10-3~6.46×10-3cm3/cm2であるリチウムイオン二次電池用正極が提供される。
本発明では、更に、下記要件
(1)正極活物質層が、30~52%の容積割合の空隙を有する
(2)リチウム含有金属酸化物の容積と導電材の容積が、1:0.06~0.23の比を有する
(3)リチウム含有金属酸化物の容積と導電材の容積の合計値が、正極活物質層の容積の40~65%の割合を有する
(4)x及びyが、0.015≦x≦0.095及び0.025≦y≦0.19の範囲である
(5)x及びyが、1:1~2の比を有する
のいずれかを備える場合、リチウムイオン二次電池のサイクル特性をより向上しうる正極及びサイクル特性がより向上したリチウムイオン二次電池を提供できる。
(I)正極
正極は、集電体と、集電体の少なくとも一方面に形成された正極活物質としてのリチウム含有金属酸化物を含む正極活物質層を備えている。
リチウム含有金属酸化物は、下記一般式(1)
LiFe1-xZrxP1-ySiyO4 (1)
(但し、0<x<1であり、0<y<1である)
で表される単位格子を有している。
また、x及びyは、サイクル特性をより向上する観点から、1:1~2の比を有することが好ましい。
一般式(1)の組成を有するほとんどのリチウム含有金属酸化物はオリビン型構造を有するが、オリビン型構造を有さない構成であってもよい。
リチウム含有金属酸化物は、0.3~30μmの平均粒子径を有していることが好ましい。より好ましい平均粒子径は、3~18μmである。
リチウム含有金属酸化物は、原料として、各元素の炭酸塩、水酸化物、塩化物、硫酸塩、酢酸塩、酸化物、シュウ酸塩、硝酸塩、アルコキシド等の組合せを用いることにより製造できる。原料には水和水が含まれていてもよい。製造方法としては、焼成法、固相法、ゾルゲル法、溶融急冷法、メカノケミカル法、共沈法、水熱法、噴霧熱分解法等の方法を用いることができる。これら方法の内、不活性雰囲気(例えば、窒素雰囲気)下での焼成法(焼成条件は、400~650℃で1~24時間)が簡便である。
リチウム含有金属酸化物は、導電性を向上するために、その表面が炭素で被覆されていてもよい。被覆は、リチウム含有金属酸化物全面でもよく、一部でもよい。
炭素の被覆方法は、特に限定されず、公知の方法を利用できる。例えば、リチウム含有金属酸化物の原料に、炭素源となる化合物を混合し、得られた混合物を不活性雰囲気下で焼成することにより被覆する方法が挙げられる。炭素源となる化合物は、原料がリチウム含有金属酸化物に変化することを妨げない化合物を使用する必要がある。そのような化合物としては、糖類では、スクロース、フルクトース等が挙げられる。あるいはポリエーテル類ではポリエチレングリコールやポリプロピレングリコール等が挙げられる。また、ポリビニルアルコールやポリアクリルアミド、カルボキシメチルセルロース、ポリ酢酸ビニル等の炭素を含有する高分子であれば使用することができる。
炭素源となる化合物は、リチウム含有金属酸化物の原料との合計に対して、5~30重量%の範囲で使用することが好ましい。
正極活物質層は、正極活物質としての上記リチウム含有金属酸化物及び導電材とを少なくとも含む。
正極活物質層は、集電体の単位面積当たり、0.82×10-3~7.87×10-3cm3/cm2の容積の空隙を有している。空隙の容積が0.82×10-3cm3/cm2未満の場合、空隙内の電解液の副反応による析出物で、リチウムの移動が阻害されることによって、サイクル特性が低下することがある。7.87×10-3cm3/cm2より大きい場合、導電パスが不十分で、レート特性が低下すると共に、電池のエネルギー密度が低下することがある。
空隙の容積は、例えば、次の方法により調整できる。空隙の容積を上げる場合は、プレス加工時のプレス間隔を大きくすることで、下げる場合は、プレス加工時のプレス間隔を小さくすることで、調整できる。
正極活物質層は、集電体の単位面積当たり、2.80×10-3~15.8×10-3cm3/cm2の容積を有していることが好ましい。容積が2.80×10-3cm3/cm2未満の場合、電極1枚当りの容量が減少するため、ある容量の電池を作製する場合に電池に含まれる集電体の枚数及びセパレータ等の部材が増加する結果、製造コストが増加するし、加えて容量密度の低下につながることがある。15.8×10-3cm3/cm2より大きい場合、集電体に電極スラリーを塗工する際に、塗工したスラリーの乾燥に時間がかかり生産性が低下することがある。より好ましい容積は4.17×10-3~13.2×10-3cm3/cm2である。
なお、上記容積は、正極活物質層中のリチウム含有金属酸化物及び導電材の平均粒子径から算出された値であり、その算出法は実施例の欄に記載する。
導電材としては、アセチレンブラック、カーボン、グラファイト、天然黒鉛、人造黒鉛、ニードルコークス等を用いることができる。
バインダー(結着剤)としては、(メタ)アクリル系樹脂、ポリテトラフルオロエチレン、ポリビニリデンフルオライド、ポリビニルクロライド、エチレンプロピレンジエンポリマー、スチレンブタジエンゴム、アクリロニトリル-ブタジエンゴム、フッ素ゴム、ポリ酢酸ビニル、ポリエチレン、ニトロセルロース等を用いることができる。
有機溶剤としては、N-メチル-2-ピロリドン、トルエン、シクロヘキサン、ジメチルホルムアミド、ジメチルアセトアミド、メチルエチルケトン、酢酸メチル、アクリル酸メチル、ジエチルトリアミン、N,N-ジメチルアミノプロピルアミン、エチレンオキシド、テトラヒドロフラン等を用いることができる。
集電体としては、連続孔を持つ発泡(多孔質)金属、ハニカム状に形成された金属、焼結金属、エキスパンドメタル、不織布、板、箔、孔開きの板、孔開きの箔等を用いることができる。
正極活物質層の厚さは、0.01~2mm程度が好ましい。厚すぎると導電性が低下し、薄すぎると単位面積当たりの容量が低下するので好ましくない。なお、塗布並びに乾燥によって得られた正極活物質層は、リチウム含有金属酸化物の充填密度を高めるためプレス等により圧縮してもよい。
本発明のリチウムイオン二次電池は、上記正極と、負極と、正極と負極との間に位置するセパレータとを備えている。
負極は、負極活物質層を備えている。
負極活物質層は公知の方法により作製できる。具体的には、正極活物質層の作製法で説明した方法と同様にして作製できる。つまり、正極活物質層の作製法で説明した結着剤と導電材と増粘剤、負極活物質と混合した後、この混合粉末をシート状に成形し、当該成形体をステンレス、銅等の導電体網(集電体)に圧着すればよい。また、上記混合粉末を正極活物質層の作製法で説明した公知の有機溶剤と混合して得られたスラリーを銅等の集電体上に塗布することにより作製することもできる。
人造黒鉛としては、メソカーボンマイクロビーズ、メソフェーズピッチ粉末、等方性ピッチ粉末等を黒鉛化して得られる黒鉛が挙げられる。また、非晶質炭素を表面に付着させた黒鉛粒子も使用できる。これらの中で、天然黒鉛は、安価でかつリチウムの酸化還元電位に近く、高エネルギー密度電池が構成できるためより好ましい。
また、リチウム遷移金属酸化物、リチウム遷移金属窒化物、遷移金属酸化物、酸化シリコン等も負極活物質として使用可能である。これらの中で、Li4Ti5O12は電位の平坦性が高く、かつ充放電による体積変化が小さいためより好ましい。
リチウムイオン二次電池は、通常、正極と負極間に非水電解質を備えている。非水電解質としては、例えば、有機電解液、ゲル状電解質、高分子固体電解質、無機固体電解質、溶融塩等を用いることができる。この内、有機電解液が、電池の製造容易性の観点から一般に使用されている。
有機電解液は、電解質塩と有機溶媒とを含む。
また、PC、EC及びブチレンカーボネート等の環状カーボネート類は高沸点溶媒であるため、GBLと混合する溶媒として好適である。
セパレータとしては、多孔質材料又は不織布等が挙げられる。セパレータの材質としては、上述した、電解質中に含まれる有機溶媒に対して溶解したり膨潤したりしないものが好ましい。具体的には、ポリエステル系ポリマー、ポリオレフィン系ポリマー(例えば、ポリエチレン、ポリプロピレン)、エーテル系ポリマー、ガラスのような無機材料等が挙げられる。
電池容器のような他の部材についても従来公知のリチウムイオン二次電池に使用される各種材料を使用でき、特に制限はない。
リチウムイオン二次電池は、例えば、正極と負極と、それらの間に挟まれたセパレータとからなる積層体を備えている。積層体は、例えば短冊状の平面形状を有していてもよい。また、円筒型や扁平型の電池を作製する場合は、積層体を巻き取ってもよい。
積層体は、その1つ又は複数が電池容器の内部に挿入される。通常、正極及び負極は電池の外部導電端子に接続される。その後に、正極、負極及びセパレータを外気より遮断するために電池容器を密閉する。
更に、金属箔に熱可塑性樹脂を貼り付けたラミネート膜で密封する方法も使用できる。
なお、密封時に電解質注入用の開口部を設けてもよい。
(正極活物質の合成)
(1)正極活物質A1
出発原料にリチウム源としてLiCH3COO、鉄源としてFe(NO3)3・9H2O、ジルコニウム源としてZrCl4、リン源としてH3PO4(85%)、シリコン源としてSi(OC2H5)4とを使用した。リチウム源であるLiCH3COOを131.96gとして、Li:Fe:Zr:P:Siがモル比で1:0.95:0.05:0.95:0.05となるように上記各原料を秤量した。これらを3LのC2H5OH(溶媒)に溶解させ、溶液を室温でスターラーにて48時間攪拌した。その後、40℃の恒温槽内にて溶液から溶媒を除去し、茶褐色の粉末を得た。
単相粉末の平均粒子径は、粒子体積の累積度が50%となる値D50を意味し、レーザー回折・散乱式粒度分布測定装置を用いて測定された値である。
正極活物質A1をメノウ乳鉢にて粉砕し、理学社製X線解析装置MiniFlexIIにより粉末X線回折パターンを得た。測定条件は電圧30kV、電流15mA、発散スリット1.25°、受光スリット0.3mm、散乱スリット1.25°、2θの範囲が10°~90°、1ステップ0.02°に設定し、最大ピークの強度が800~1500になるようにステップ毎の計測時間を調整した。次に、得られた粉末X線回折パターンについて、「RIETAN-FP」(F. Izumi and K. Momma, "Three-dimensional visualization in powder diffraction," Solid State Phenom., 130, 15-20 (2007))を用いて、表1に示すパラメータを初期値として「ins」ファイルを作成し、「DD3.bat」を使用してリートベルト解析による構造解析を行い、「.lst」ファイルより、各パラメータを読み取り、格子定数を決定した(S値(収束度合)は1.1~1.3)
Li:Fe:Zr:P:Siがモル比で1:0.975:0.025:0.975:0.025となるように各原料を秤量したこと以外は正極活物質A1と同様にして正極活物質A2(平均粒子径9.2μm及び真密度3.45g/cm3)を得た。得られた正極活物質A2の格子定数は(a,b,c)=(10.330,6.008,4.694)であった。
Li:Fe:Zr:P:Siがモル比で1:0.975:0.025:0.95:0.05となるように各原料を秤量したこと以外は正極活物質A1と同様にして正極活物質A3(平均粒子径9.2μm及び真密度3.45g/cm3)を得た。得られた正極活物質A3の格子定数は(a,b,c)=(10.327,6.007,4.693)であった。
Li:Fe:Zr:P:Siがモル比で1:0.965:0.035:0.965:0.035となるように各原料を秤量したこと以外は正極活物質A1と同様にして正極活物質A4(平均粒子径9.2μm及び真密度3.45g/cm3)を得た。得られた正極活物質A4の格子定数は(a,b,c)=(10.326,6.007,4.693)であった。
Li:Fe:Zr:P:Siがモル比で1:0.905:0.095:0.81:0.19となるように各原料を秤量したこと以外は正極活物質A1と同様にして正極活物質A5(平均粒子径9.2μm及び真密度3.45g/cm3)を得た。得られた正極活物質A5の格子定数は(a,b,c)=(10.335,6.012,4.714)であった。
Li:Fe:Zr:P:Siがモル比で1:0.985:0.015:0.97:0.03となるように各原料を秤量したこと以外は正極活物質A1と同様にして正極活物質A6(平均粒子径9.2μm及び真密度3.45g/cm3)を得た。得られた正極活物質A6の格子定数は(a,b,c)=(10.326,6.006,4.685)であった。
市販のLiFePO4(住友大阪セメント社製)を正極活物質A7(平均粒子径9.2μm及び真密度3.45g/cm3)とした。正極活物質A7の格子定数は(a,b,c)=(10.325,6.004,4.683)であった。
Li:Fe:Zr:P:Siがモル比で1:0.9:0.1:0.8:0.2となるように各原料を秤量したこと以外は正極活物質A1と同様にして正極活物質A8(平均粒子径9.2μm及び真密度3.45g/cm3)を得た。得られた正極活物質A5の格子定数は(a,b,c)=(10.337,6.015,4.720)であった。
Li:Fe:Zr:P:Siがモル比で1:0.925:0.075:0.85:0.15となるように各原料を秤量したこと以外は正極活物質A1と同様にして正極活物質A9(平均粒子径9.2μm及び真密度3.45g/cm3)を得た。得られた正極活物質A6の格子定数は(a,b,c)=(10.338,6.005,4.691)であった。
表2に正極活物質の原料のZr/Siモル比、格子定数、真密度及び平均粒子径をまとめて示す。
(1)正極
上記正極活物質A1、アセチレンブラック(導電材、平均粒子径0.035μm、真密度1.8g/cm3、電気化学工業社製)、アクリル系樹脂(バインダー、固形分濃度29.9重量%、JSR社製)、カルボキシメチルセルロース(増粘剤、第一工業製薬社製)を、100:6:27:1.2の重量(g)で、フィルミックス80-50型(プライミクス社製)を用いて室温下で78.8gのイオン交換水と攪拌混合することで、水性の正極ペーストを得た。この正極ペーストを、圧延アルミニウム箔(厚さ:20μm)の両面上にダイコーターを用いて塗布した。片面塗布量(固形分)は、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で5:0.30:0.35:0.003mg/cm2であった。得られた塗膜を、空気中100℃で10分間乾燥し(乾燥時厚さ68μm)、プレス加工することで、集電体上に厚さ48μmの正極活物質層を備えた正極P1(塗工面サイズ:28mm(縦)×28mm(横))を得た。
正極活物質の容積と導電材の容積の合計値は1.62×10-3cm3/cm2であり、正極活物質層の空隙の容積は0.84×10-3cm3/cm2であった。
(i)正極活物質の容積は、その平均粒子径と、集電体の単位面積当たりの正極活物質の粒子数の積算値を意味する。
(ii)導電材の容積は、その平均粒子径と、集電体の単位面積当たりの正極活物質の粒子数の積算値を意味する。導電材の平均粒子径は、正極活物質と同様の方法で得られた値を意味する。
(iii)正極活物質層の空隙の容積は、正極活物質層の容積から、この層を構成する固形分である正極活物質及び導電材の容積を差し引いて得られる値を意味する。正極活物質層の容積は、この層の厚さ×縦×横の積算値を意味する。
天然黒鉛(日立化成工業社製)、スチレンブタジエンゴム(バインダー、固形分濃度40.1重量%、日本ゼオン社製)、カルボキシメチルセルロース(増粘剤、ダイセル社製)を、100:2:1の重量(g)で、2軸遊星プラネタリミキサー(プライミクス社製)を用いて100gのイオン交換水と室温下で攪拌混練することで、水性の負極ペーストを得た。この負極ペーストを、圧延銅箔(厚さ:10μm)の片面上にダイコーターを用いて塗布した。得られた塗膜を、空気中100℃で10分間乾燥し、プレス加工することで、集電体上に厚さ20μmの負極活物質層を備えた負極(塗工面サイズ:30mm(縦)×30mm(横))を得た。
図1(a)に示す手順で図1(b)に示す電池を作製した。
まず、正極1及び負極2を130℃で24時間減圧乾燥した後に、ドライAr雰囲気下のグローボックス内に入れた。次に、正極1に接着フィルム3付きのアルミニウム製タブリード4を、負極2に接着フィルム5付きのニッケル製のタブリード6をそれぞれ超音波溶接した。グローボックス内で、負極2の塗工面7が隠れるようにセパレータ(微多孔膜、サイズ:30mm(縦)×30mm(横)×25μm(厚さ)、ポリポア社製)9を積載し、塗工面が中心に重なるように正極1を重ね単セル10を作製した。8は正極1の塗工面を意味する。
なお、電解液の注液量は、各電池で使用する電極の厚さ(正極と負極の合計値)に準じて適宜決定しており、実際に作製した電池の正極、負極及びセパレータに電解液が十分浸透する量とした。
正極活物質A2を使用し、正極活物質層の空隙の容積を1.56×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
(実施例3)
正極活物質A3を使用し、正極活物質層の空隙の容積を1.76×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
正極活物質A4を使用し、片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で8:0.48:0.56:0.005mg/cm2とし、正極活物質層の空隙の容積を2.86×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
(実施例5)
正極活物質A5を使用し、片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で8:0.48:0.56:0.005mg/cm2とし、正極活物質層の空隙の容積を2.86×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で14.2:0.85:0.99:0.009mg/cm2とし、正極活物質層の空隙の容積を5.07×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
(実施例7)
正極活物質A6を使用し、片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で12:0.72:0.83:0.008mg/cm2とし、正極活物質層の空隙の容積を4.57×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で18.4:1.10:1.28:0.012mg/cm2とし、正極活物質層の空隙の容積を7.84×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
(実施例9)
片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で19.8:1.19:1.38:0.012mg/cm2とし、正極活物質層の空隙の容積を7.22×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
正極活物質層の空隙の容積を0.66×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
(比較例2)
片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で18.4:1.10:1.28:0.012mg/cm2とし、正極活物質層の空隙の容積を7.97×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で21:1.26:1.46:0.13mg/cm2とし、正極活物質層の空隙の容積を7.03×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
(比較例4)
正極活物質A7を使用し、片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で8.0:0.48:0.56:0.005mg/cm2とし、正極活物質層の空隙の容積を2.86×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
正極活物質A8を使用し、片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で8.0:0.48:0.55:0.005mg/cm2とし、正極活物質層の空隙の容積を2.85×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
(比較例6)
正極活物質A9を使用し、片面塗布量(固形分)を、正極活物質、アセチレンブラック、アクリル系樹脂、カルボキシメチルセルロースの順で12.0:0.72:0.83:0.008mg/cm2とし、正極活物質層の空隙の容積を4.57×10-3cm3/cm2とすること以外は、実施例1と同様にして電池を得た。
(1)レート特性 作製した電池を25℃環境下で0.1Cで3.6Vまで充電し、0.1Cで2.0Vまで放電し、0.1C容量を、0.1Cで3.6Vまで充電し、1Cで2.0Vまで放電することで、1C容量を測定し、レート特性(1C/0.1C)を算出した。なお、正極の理論容量から算出される容量を1時間で充電又は放電する電流を1Cとした。
作製した電池を25℃環境下で1Cで3.6Vまで充電し、1Cで2.0Vまで放電する過程を1サイクルとし、3500サイクル繰り返し、1サイクル目の放電容量と3500サイクル目の放電容量を比較することで3500サイクルでのサイクル特性を算出した。
得られた結果を、表3に示す。
Claims (9)
- 集電体と、前記集電体の少なくとも一方面に形成された正極活物質層とを備え、
前記正極活物質層が、下記一般式(1)
LiFe1-xZrxP1-ySiyO4 (1)
(但し、0<x<1であり、0<y<1である)
で表される単位格子を有するリチウム含有金属酸化物と、導電材とを含む層であり、集電体の単位面積当たり、0.82×10-3~7.87×10-3cm3/cm2の容積の空隙を有し、
前記単位格子が、10.326≦a≦10.335、6.006≦b≦6.012、4.685≦c≦4.714の格子定数を有し、
前記リチウム含有金属酸化物の容積と導電材の容積の合計値が、集電体の単位面積当たり、1.61×10-3~6.46×10-3cm3/cm2であるリチウムイオン二次電池用正極。 - 前記リチウム含有金属酸化物の容積は、集電体の単位体積あたり、1.40×10-3~5.80×10-3cm3/cm2である請求項1に記載のリチウムイオン二次電池用正極。
- 前記導電材の容積は、集電体の単位体積あたり、0.16×10-3~0.67×10-3cm3/cm2である請求項1または2に記載のリチウムイオン二次電池用正極。
- 前記リチウム含有金属酸化物の容積と導電材の容積が、1:0.06~0.23の比を有する請求項1~3のいずれか1つに記載のリチウムイオン二次電池用正極。
- 前記リチウム含有金属酸化物の容積と導電材の容積の合計値は、前記正極活物質層の容積の40~65%の割合である請求項1~4のいずれか1つに記載のリチウムイオン二次電池用正極。
- 前記x及びyが、0.015≦x≦0.095及び0.025≦y≦0.19の範囲である請求項1~5のいずれか1つに記載のリチウムイオン二次電池用正極。
- 前記x及びyが、1:1~2の比を有する請求項1~6のいずれか1つに記載のリチウムイオン二次電池用正極。
- 前記正極活物質層は更にバインダーと増粘剤を含み、前記バインダーはアクリル系樹脂であり、前記増粘剤はカルボキシメチルセルロースであり、前記導電材はアセチレンブラックであり、
集電体単位面積当たりの前記正極活物質、前記アセチレンブラック、前記アクリル樹脂と前記カルボキシメチルセルロースのそれぞれの容積が、5~19.8、0.3~1.19、0.35~1.38、0.003~0.012mg/cm2である請求項6又は7に記載のリチウムイオン二次電池用正極。 - 請求項1~8のいずれか1つに記載の正極と、負極と、前記正極と前記負極との間に位置するセパレータとを備えたリチウムイオン二次電池。
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- 2014-04-23 US US14/782,492 patent/US9735420B2/en not_active Expired - Fee Related
- 2014-04-23 CN CN201480021812.2A patent/CN105122508B/zh not_active Expired - Fee Related
- 2014-04-23 WO PCT/JP2014/061474 patent/WO2014175352A1/ja active Application Filing
- 2014-04-23 JP JP2015513815A patent/JP6416082B2/ja not_active Expired - Fee Related
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US9735420B2 (en) | 2017-08-15 |
CN105122508B (zh) | 2018-04-06 |
JP6416082B2 (ja) | 2018-10-31 |
US20160056453A1 (en) | 2016-02-25 |
JPWO2014175352A1 (ja) | 2017-02-23 |
CN105122508A (zh) | 2015-12-02 |
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